Characteristics of life…

2. Characteristics of life… • Order (organization) • Reproduction • Growth & Development • Energy utilization • Response to environment • Homeostasis (regulation) • Evolutionary adaptation 

5. Emergent properties • Life’s basic characteristic is a high degree of order. • Biological organization is based on a hierarchy of structural levels, each building on the levels below. • At the lowest level are atoms that are ordered into complex biological molecules. • Many molecules are arranged into minute structure called organelles, which are the components of cells.

6. Cells are the subunits of organisms, the units of life. • Some organisms consist of a single cells, others are multicellular aggregates of specialized cells. • Whether multicellular or unicellular, all organisms must accomplish the same functions: uptake and processing of nutrients, excretion of wastes, response to environmental stimuli, and reproduction among others.

7. Multicellular organisms exhibit three major structural levels above the cell: similar cells are grouped into tissues, several tissues coordinate to form organs, and several organs form an organ system. • For example, to coordinate locomotory movements, sensory information travels from sense organs to the brain, where nervous tissues composed of billions of interconnected neurons, supported by connective tissue, coordinate signals that travel via other neurons to the individual muscle cells.

8. Organisms belong to populations, localized group of organisms belonging to the same species. • Populations of several species in the same area comprise a biological community. • These populations interact with their physical environment to form an ecosystem.

9. Investigating biology at its many levels is fundamental to the study of life. • Biological processes often involve several levels of biological organization. • The coordinated strike of a rattlesnake at a mouse requires complex interactions at the molecular, cell, tissue, and organ levels within its body. • The outcome impacts not only the well-being of the snake and the mouse but also the populations of both with implications for their biological community. • Many biologists study life at one level but gain a broader perspective when they integrate their discoveries with processes at other levels.

10. New properties emerge at each step upward in the biological hierarchy. • These emergent properties result from interactions between components. • A cell is much more than a bag of molecules. • This theme of emergent properties accents the importance of structural arrangement. • The emergent properties of life are not supernatural, but simply reflect a hierarchy of structural organization.

11. Reductionism • The complex organization of life presents a dilemma to scientists seeking to understand biological processes. • We cannot fully explain a higher level of organization by breaking down to its parts. • At the same time, it is futile to try to analyze something a complex as an organism or cell without taking it apart. • Reductionism, reducing complex systems to simpler components, is a powerful strategy in biology. • Reductionism is balanced by the longer-range objective of understanding emergent properties.

12. Cell theory • The cell theory postulates that all living things consist of cells. • The cell theory has been extended to include the concept that all cells come from other cells. • New cells are produced by division of existing cells, the critical process in reproduction, growth, and repair of multicellular organisms.

13. Prokaryotes & Eukaryotes • All cells are enclosed by a membrane that regulates the passage of materials between the cell and its surroundings. • At some point, all cells contain DNA, the heritable material that directs the cell’s activities. • Two major kinds of cells - prokaryotic cells and eukaryotic cells - can be distinguished by their structural organization. • The cells of the microorganisms called bacteria and archaea are prokaryotic. • All other forms of life have the more complex eukaryotic cells.

14. Eukaryotic cells are subdivided by internal membranes into functionally-diverse organelles. • Also, DNA combines with proteins to form chromosomes within the nucleus. • Surrounding the nucleus is the cytoplasm which contains a thick cytosol and various organelles. • Some eukaryotic cells have external cell walls.

16. In contrast, in prokaryotic cells the DNA is not separated from the cytoplasm in a nucleus. • There are no membrane-enclosed organelles in the cytoplasm. • Almost all prokaryotic cells have tough external cell walls. • All cells, regardless of size, shape, or structural complexity, are highly ordered structures that carry out complicated processes necessary for life.

17. DNA • Biological instructions for ordering the processes of life are encoded in DNA (deoxyribonucleic acid). • DNA is the substance of genes, the units of inheritance that transmit information from parents to offspring.

18. Each DNA molecule is composed of two long chains arranged into a double helix. • The building blocks of the chain, four kinds of nucleotides, convey information by the specific order of these nucleotides.

19. All forms of life employ the same genetic code. • The diversity of life is generated by different expressions of a common language for programming biological order. • As a cell prepares to divide, it copies its DNA and mechanically moves the chromosomes so that the DNA copies are distributed equally to the two “daughter” cells. • The continuity of life over the generations and over the eons has its molecular basis in the replication of DNA.

20. The entire “library” of genetic instructions that an organism inherits is called its genome. • The genome of a human cell is 3 billion chemical letters long. • The “rough draft” of the sequence of nucleotides in the human genome was published in 2001. • Biologists are learning the functions of thousands of genes and how their activities are coordinated in the development of an organism.

22. Negative feedback • A negative-feedback system keeps the body temperature of mammals and birds within a narrow range in spite of internal and external fluctuations. • A “thermostat” in the brain controls processes that holds the temperature of the blood at a set point. • When temperature rises above the set point, an evaporative cooling system cools the blood until it reaches the set point at which the system is turned off. • If temperature drops below the set point, the brain’s control center inactivates the cooling systems and constricts blood to the core, reducing heat loss. • This steady-state regulation, keeping an internal factor within narrow limits, is called homeostasis.

23. Positive feedback • While positive feedback systems are less common, they do regulate some processes. • For example, when a blood vessel is injured, platelets in the blood accumulate at the site. • Chemicals released by the platelets attract more platelets. • The platelet cluster initiates a complex sequence of chemical reactions that seals the wound with a clot. • Regulation by positive and negative feedback is a pervasive theme in biology.

25. Domains/taxonomy • Until the last decade, biologists divided the diversity of life into five kingdoms. • New methods, including comparisons of DNA among organisms, have led to a reassessment of the number and boundaries of the kingdoms. • Various classification schemes now include six, eight, or more kingdoms. • Also coming from this debate has been the recognition that there are three even higher levels of classifications, the domains. • The three domains are the Bacteria, Archaea, and Eukarya.

26. Taxonomy • In the face of this complexity, humans are inclined to categorize diverse items into a smaller number of groups. • Taxonomy is the branch of biology that names and classifies species into a hierarchical order.

27. Both Bacteria and Archaea have prokaryotes. • Archaea may be more closely related to eukaryotes than they are to bacteria. • The Eukarya includes at least four kingdoms: Protista, Plantae, Fungi, and Animalia.

28. The Plantae, Fungi, and Animalia are primarily multicellular. • Protista is primarily unicellular but includes the multicellular algae in many classification schemes. • Most plants produce their own sugars and food by photosynthesis. • Most fungi are decomposers that break down dead organisms and organic wastes. • Animals obtain food by ingesting other organisms.

29. Underlying the diversity of life is a striking unity, especially at the lower levels of organization. • The universal genetic language of DNA unites prokaryotes, like bacteria, with eukaryotes, like humans. • Among eukaryotes, unity is evident in many details of cell structure.

30. Charles Darwin brought biology into focus in 1859 when he presented two main concepts in The Origin of Species. • The first was that contemporary species arose from a succession of ancestors through “descent with modification” (evolution). • The second was that the mechanism of evolution is natural selection. • Natural Selection (and artificial selection)

31. Darwin synthesized natural selection by connecting two observations. • Observation 1: Individuals in a population of any species vary in many heritable traits. • Observation 2: Any population can potentially produce far more offspring than the environment can support. • This creates a struggle for existence among variant members of a population. • Darwin inferred that those individuals with traits best suited to the local environment will generally leave more surviving, fertile offspring. • Differential reproductive success is natural selection.

33. Natural selection, by its cumulative effects over vast spans of time, can produce new species from ancestral species. • For example, a population may be fragmented into several isolated populations in different environments. • What began as one species could gradually diversify into many species. • Each isolated population would adapt over many generations to different environmental problems

34. The finches of the Galapagos Islands diversified after an initial colonization from the mainland to exploit different food sources on different islands.

35. Descent with modification accounts for both the unity and diversity of life. • In many cases, features shared by two species are due to their descent from a common ancestor. • Differences are due to modifications by natural selection modifying the ancestral equipment in different environments. • Evolution is the core theme of biology - a unifying thread that ties biology together.

36. Experiments & control groups… • We test the hypothesis by performing the experiment to see whether or not the results are as predicted. • Deductive logic takes the form of “If…then” logic.

37. The research by David Reznick and John Endler on differences between populations of guppies in Trinidad is a case study of the hypothetico-deductive logic. • Guppies, Poecilia reticulata, are small fish that form isolated populations in small streams. • These populations are often isolated by waterfalls. • Reznick and Endler observed differences in life history characteristics among populations. • These include age and size at sexual maturity.

38. Guppies! • Variation in life history characteristics are correlated with the types of predators present. • Some pools have a small predator, a killifish, which preys predominately on juvenile guppies. • Other pools have a larger predator, a pike-cichlid, which preys on sexually mature individuals. • Guppy populations that live with pike-cichlids are smaller at maturity and reproduce at a younger age on average than those that coexist with killifish. • However, the presence of a correlation does not necessarily imply a cause-and-effect relationship. • Some third factor may be responsible…

39. These life history differences may be due to differences in water temperature or to some other physical factor. • Hypothesis 1: If differences in physical environment cause variations in guppy life histories • Experiment: and samples of different guppy populations are maintained for several generation in identical predator-free aquaria, • Predicted result: then the laboratory populations should become more similar in life history characteristics. • The differences among populations persisted for many generations, indicating that the differences were genetic.

40. Reznick and Endler tested a second explanation. • Hypothesis 2: If the feeding preferences of different predators caused contrasting life histories in different guppy populations to evolve by natural selection, • Experiment: and guppies are transplanted from locations with pike-cichlids (predators on adults) to guppy-free sites inhabited by killifish (predators on juveniles), • Predicted Results: then the transplanted guppy populations should show a generation-to-generation trend toward later maturation and larger size. • After 11 years (30 to 60 generations) the transplanted guppies were 14% heavier at maturity and other predicted life history changes were also present.

41. Reznick and Endler used a transplant experiment to test the hypothesis that predators caused life history difference between populations of guppies.

42. Reznick and Endler used controlled experiments to make comparisons between two sets of subjects - guppy populations. • The set that receives the experimental treatment (transplantation) is the experimental group. • The control group were guppies who remained in the pike-cichlid pools. • Such a controlled experiment enables researchers to focus on responses to a single variable. • Without a control group for comparison, there would be no way to tell if it was the killifish or some other factors that caused the populations to change.

43. Based on these experiments, Reznick and Endler concluded that natural selection due to differential predation on larger versus smaller guppies is the most likely explanation for the observed differences in life history characteristics. • Because pike-cichlids prey preferentially on mature adults, guppies that mature at a young age and smaller size will be more likely to reproduce at least one brood before reaching the size preferred by the predator. • The controlled experiments documented evolution under natural settings in only 11 years. • This study reinforces the important point that scientific hypotheses must be testable.

44. 1. Diagram the hierarchy of structural levels in biology from atoms to organism, and population to biosphere.

46. With each step up in biological hierarchy, new properties EMERGE that were not there at simpler levels Order (organization) Reproduction Growth & Development Energy utilization Response to environment Homeostasis (regulation) Evolutionary adaptation  2. Explain the concept of “emergent properties” and list a few examples.

47. Holism The principle that a higher level of order cannot be meaningfully explained by examining parts alone Look at the ‘WHOLE’ Reductionism A complex system can be understood by studying it’s component parts Look at the ‘REDUCED PARTS’  3. What is reductionism? Why is it used in Biology?

48. 4.Explain how the invention of microscopes contributed to the formulation of the cell theory and our current knowledge of the cell. • Microscopes allowed us to see microorganisms, cells, and the complex structure of cells. • Cell Theory: 1. all cells come from other cells 2. cells dividing is the basis for all reproduction and growth 

49. Prokaryotic Lacks membrane-bound organelles Small Circular DNA Probable first cells Ex: Bacteria, Archaea Eukaryotic Has membrane-bound nucleus and organelles Much larger than prokaryotes Strand DNA Ex: Protist, Plant, Fungi and Animal cells  5. Distinguish between prokaryotic and eukaryotic cells.

50. 6. Explain, in your own words, what is meant by “form fits function”. • Biological structure gives clues about what it does and how it works • Knowing a structure’s function gives insights about its construction 